3.2.4 Cell Recognition And Immune System Flashcards
What is an antigen?
molecules that generate an immune response when detected by the body - usually proteins found on the surface of cells
What is a foreign antigen?
antigens that aren’t normally found in the body - the immune system responds to these types of pathogens
antigens allow the immune system to identify:
- pathogens
- abnormal body cells
- toxins
- cells from other individuals of the same species
What are pathogens?
microorganisms that cause disease (e.g. bacteria, virus, fungi) which have antigens on their surface so are identified as foreign by immune system.
what are abnormal body cells?
cancerous/pathogen infected cells have abnormal antigens on their surface which are identified as foreign by the immune system
What are toxins?
poison molecules which are antigens themselves - immune system responds to toxins & pathogens that produced them
what are Cells from other individuals of the same species?
receiving cells from another person (blood transfusion/organ transplant) will have antigens that are different - these are detected as foreign antigens by the immune system which leads to rejection of organ transplant if immunosuppressant drugs are not taken. i
phagocytosis (definition)
A type of endocytosis in which a cell engulfs large particles or whole cells
What is a phagocyte?
A white blood cell that destroys pathogens by engulfing them and breaking them down
phagocytosis process
1) phagocyte recognises foreign antigens.
2) cytoplasm of phagocyte engulfs pathogen.
3) pathogen is contained within a phagocytic vacuole.
4) a lysosome (containing lysozymes) fuses with the phagocytic vacuole.
5) lysozymes break down pathogen.
6) phagocyte presents pathogens antigens on its surface to activate other immune cells.
what are the 4 stages in immune response?
1: phagocytosis
2: activation of T-cells (by phagocytes)
3: activation of B-cells (by T-helper cells) which divide into plasma cells
4: plasma cells make more antibodies specific to an antigen.
What is a lymphocyte?
white blood cell found in blood stream & made in bone marrow
types of lymphocytes
T cells and B cells
function of t cells
Receptor proteins on surface bind to antigens presented to it by phagocytes. T-helper cells release chemical signals that activate and stimulate phagocytosis. Cytoxic T-cells kill abnormal and foreign cells.
function of b cells
Produces plasma cells and memory cells
plasma cells are:
- Identical to B-cells
- secrete antibodies
process of humoral response
1) pathogen engulfed and destroyed by phagocyte, which displays antigens on its surface
2) receptors on T helper cells that are complementary bind to the antigens on the surface of the phagocyte, which stimulates the T helper cells to divide by mitosis to form clones
3) a B cell presents the antigens of the encountered pathogen on its surface OR the receptors on the B cell are complementary to the antigens so the antigens are then displayed on the surface of the B cell
4) the T helper cells (previously activated by the same pathogen) attach to the B cell by its complementary receptors
5) the binding of the T helper cell causes the B cell to divide via mitosis, producing clones of plasma cells and memory cells
6) memory cells remain in the bloodstream for a second response and plasma cells secrete antibodies which attach to the antigens and initiate chemical destruction
Antibodies (definition)
proteins that recognise and bind to specific antigens to form antibody-antigen complexes
structure of an antibody
proteins made by B-cells
- contains four polypeptide chains
- 2 heavy
- 2 light
- 2 antigen binding site
functions of antibodies
- immobilise bacteria by attacking flagella
- prevent entry of viruses/toxins into cell
- agglutinate bacteria (stick together in clumps)
- make membrane channels with complement proteins to allow water to enter bacteria by osmosis
- coat bacteria, identifying them for phagocytosis
- neutralise toxins
polyclonal antibodies are:
a series of antibodies are produced responding to a variety of different sites on the antigen
monoclonal antibodies are:
a collection of identical antibodies that interact with a single antigen site
primary response
first time the immune system combats a particular foreign substance so response is slow as there are not many B cells to respond to the antigen. When antibodies are made, B & T cells produce memory cells which remain in bloodstream
secondary response
later interactions with the same foreign substance; faster and more effective due to memory cells activated and dividing into correct antibody producing plasma cells
monoclonal antibodies in anti-cancer drugs
- cancer cells have antigens on their surface called tumour markers (not found on normal body cells)
- monoclonal antibodies that will bind to tumour markers can be made, and can have anti-cancer drugs attached
- when the monoclonal antibodies come into contact with cancer cells, they will bind to tumour markers as they are complementary
- the drug will only agglutinate (stick) in the body where there are cancer cells
monoclonal antibodies in pregnancy tests
1) urine is applied to the application area (contains complementary antibodies to hCG protein, bound to blue beads) any hCG (hormone found in urine of pregnant women) will bind to the antibody on the beads
2) The urine moves up the stick, carrying the beads with it
3) The urine moves to the test strip (containing immobilised antibodies complementary to hCG)
4) if hCG is present, immobilised antibodies stick to the hCG with blue beads attached so the strip turns blue
5) if no hCG is present, the beads pass the strip without binding so no colour change
ELISA (enzyme-linked immunosorbent assay) test
- allows you to see if a patient has any antibodies to an antigen or an an antigen to an antibody
- an antibody has an enzyme attached which reacts with a substrate to produce a coloured product, which causes the solution to change colour
direct ELISA (definition)
uses a single antibody that is complementary to the antigen being tested for
direct ELISA process
- antigens from a patient sample are bound to the inside of a well in a well plate
- a detection antibody with an enzyme attached that is complementary to the antigen is added (if antigen is present in sample, it will be immobilised in the walls of the well and the detection antibody will bind to it)
- the well is washed to remove any unbound antibodies
- substrate is added
- if detection antibody is present, the enzyme reacts with the substrate to produce a colour change
indirect ELISA
uses 2 antibodies
indirect ELISA process
- HIV antigen is bound to bottom of well in well plate
- a sample of patient blood plasma is added to the well (any HIV specific antibodies will bind to HIV antigen on bottom of well)
- well is washed
- secondary antibody with specific enzyme attached is added to well (can bind to HIV specific (primary) antibody)
- well is washed to remove any unbound secondary antibody
- a solution is added to the well which contains a substrate that is able to react with the enzyme and produce a coloured product (indicates patient is HIV positive)
negative ethical issues with monoclonal antibodies
HUMANS
- some deaths
- side effects
- expensive to produce
- testing new drugs presents concerns
MICE
- induced cancer
- immune system enhancers painful
- priming agent causes infections
- mice exploited and then die
positive ethical issues with monoclonal antibodies
- antibodies generated on a large scale
- saves money on NHS treatments
- can diagnose earlier than some other treatments
- may have less severe side effects
What is active immunity?
immune system makes its own antibodies after being stimulated by an antigen
- requires exposure to antigen
- takes a long time for protection to develop
- produces memory cells
- protection is long term
Active natural immunity occurs when
When you become immune after catching a disease
What is active artificial immunity?
when you become immune after being given a vaccination
What is passive immunity?
given antibodies made by a different organism
passive natural immunity example
transfer of antibodies from a mother to her fetus through placenta or breast milk
passive artificial immunity example
When you become immune after being injected with antibodies from someone else e.g. blood donations
vaccination process
- a dead/attenuated form of a pathogen is injected into body but is unable to cause major harm
- B cells respond to pathogen and release antobodies which are complementary to antigen
- antibodies become attached to antigen and agglutinate
- phagocytes engulf antigens ad enzymes break down the agglutination
- some B cells remain in blood as memory cells for the next infection
key features of a vaccination programme
- economically available in enough bulk to immunise all vulnerable population
- few side effects
- ability to produce, transport & store vaccine in a safe and hygienic way
- skilled staff to administer vaccine in many places in area
- ability to create herd immunity
What is herd immunity?
vaccines protect individuals that have them and because of the occurrence of the disease, those not vaccinated are less likely to catch the disease (protects vulnerable individuals)
why vaccination programmes don’t always work
- vaccines always contain antigens which may be free or agglutinated to pathogen
- vaccines may be injected or taken orally - orally taking vaccines increases the chance of the vaccine being broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into blood
- vaccines cannot eliminate a disease because some people have defective immune systems, an individual may develop the disease before they are immune, pathogen’s antigens can mutate, some people refuse to have vaccines for ethical, medical or religious reasons
ethical issues associated with vaccines
- all vaccines tested on animals before tested on humans
- animal based substances may be used to produce a vaccine
- testing vaccines on humans may be risky and they may put themselves at unnecessary risk
- some people don’t want to take the vaccine due to side effects but are still protected by herd immunity and others don’t think this is fair
- if there was an epidemic of a new disease there would be a rush to receive a vaccine and important questions about who would receives the vaccine first would have to be answered
What is antigenic variation?
Pathogens alter their surface antigens (and antibodies are rendered ineffective)
- memory cells will not recognise pathogen on second infection so body will have to undergo primary response again
- hard to develop vaccines against some pathogens e.. influenza
HIV (human immunodeficiency virus)
the retrovirus that attacks the human immune system and causes AIDS.
AIDS (acquired immune deficiency syndrome)
a life-threatening, sexually transmitted infection caused by (HIV) where the immune system deteriorates and eventually fails, increasing vulnerability to simple infections. AIDS is developed when T cell numbers drop critically low
Infection process of HIV
infects and eventually kills T helper cells which act as host cells so immune system is unable to mount effective response to infections which result in ill health
Initial infection of HIV
HIV replicates quickly and the infected person may experience severe flu like symptoms
latency period of HIV
HIV replication drops to a low level where no symptoms are experienced
symptoms of AIDS
unexplained weight loss, rare forms of pneumonia, rare cancers and infections not found in healthy human populations
HIV and AIDS
HIV turns into AIDS when T cell numbers drop critically low - the length of time before infection with HIV and development of AIDS differs between individuals but untreated, is often 10 years
symptoms in early stages of AIDS
minor infections of mucous membranes and reoccurring respiratory conditions
symptoms as AIDS progresses
patients more susceptible to simple infections e.g. chest infections
symptoms in late stages of AIDS
develop a range of serious infections due to very low number of immune system cells, which are likely to kill
Structure of HIV
- Attachment protein
- enevelope (extra outer layer made from host cell membrane)
- capsid (outer protein coat of virus)
- genetic material
- reverse transcriptase
HIV replication process
1) attachment proteins attach to receptor molecule on cell surface membrane of host T helper cell
2) capsid is released into cell where it uncoats and releases RNA into cytoplasm
3) inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
4) a double strand of DNA is made and inserted into host cell’s DNA
5) host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
6) viral proteins are assembled into the new viruses which bud from the cell and go to infect other cells
Why antibiotics don’t work on viruses
- antibiotics only designed to target bacterial enzymes/ribosomes not human - the virus does not have any of its own as it uses the host cells’ so antibiotics cannot inhibit them from completing metabolic reactions
- some antibiotics work by preventing bacteria from making a normal cell wall of murein so that it bursts under osmotic pressure, but viruses have a protein coat instead of a cell wall
Controlling HIV infection
no cure/vaccine but progression can be slowed with antiviral drugs
best way is to reduce its spread
ways HIV can be spread
- unprotected sex by contact of bodily fluids
- HIV positive mother in pregnancy to her fetus (not all babies are born infected and antivirals can be taken in pregnancy to reduce the risk of the baby having the infection)
How are B-cells formed?
- when antibodies on surface meet complimentary shaped antigen it binds. (Antigen-antibody complex)
- This and substances released from T-helper cell activates B-cells. (Clonal selection)
3: B-cell divides into plasma cells
